A method is described for measuring oxygen consumption of small animals. It was used for 151 newborn rabbits delivered on the 27th, 28th, 29th, and 30th day of gestation. Half of the neonates were given a pharyngeal deposition of a concentrated surfactant (SA) suspension prior to their first breath. The remaining neonates served as controls. The survival rate among the immature rabbits treated with SA was significantly higher. The treatment did not affect oxygen consumption in any age-group. With increasing maturity, the neonates consumed more oxygen, and the controls delivered on the 30th day of gestation consumed 29.6 ± SEM 4.2 ml oxygen per kilogram and minute.